CH617167A5 - Process for the preparation of alkoxylated aliphatic aldehydes and ketones - Google Patents

Abstract

Aliphatic aldehydes and ketones containing an alkoxy residue in position ss or delta with respect to the carbonyl group are prepared by reaction of an acetal of an aliphatic aldehyde or ketone with an enoxysilane derived from an enolisable aliphatic aldehyde or ketone, in the presence of a catalyst taken from the group formed by the zinc halides, boron trifluoride and its complexes, the reaction not requiring the use of low reaction temperatures nor of stoichiometric amounts of catalyst. This process is suitable in particular for the preparation of terpenic ss- or delta -methoxy- or -ethoxyaldehydes or ketones, such as 3,7,11-trimethyl-5-ethoxy-2,6,10-dodecatrienal.

Description

The present invention therefore relates to a process for the condensation of aldehyde and aliphatic ketone acetals with the enoxysilanes derived from aldehydes and aliphatic ketones giving access to alkoxylated aldehydes or ketones, not involving the use of low temperatures and stoichiometric amounts of catalyst.

More specifically, the subject of the present invention is a process for the preparation of ketones and aliphatic aldehydes comprising, in position β or 5 relative to the carbonyl group, an alkoxy residue, by reaction of an acetal of an aldehyde or of an aliphatic ketone with an enoxysilane derived from an aliphatic aldehyde or ketone which can be dissolved in the presence of a catalyst, characterized in that one uses a catalyst taken from the group formed by zinc halides, boron trifluoride and its complexes.

It has surprisingly been found that the abovementioned catalysts allow the reaction of acetals and enoxysilanes to be easily carried out without resorting to the use of low temperatures and stoichiometric amounts of catalysts.

More specifically still, the present invention relates to a process for the preparation of aliphatic carbonyl compounds comprising at least one alkoxy group, corresponding to the general formulas:

R_ R,

(I)

The present invention relates to a process for the preparation of ketones and aliphatic aldehydes having an ether function, by reaction of an aliphatic acetal with an enolic derivative of an aliphatic carbonyl compound.

More specifically, the present invention relates to a process for the preparation of aliphatic aldehydes and ketones, and in particular of those of these compounds comprising one or more double bonds having one or more alkyloxy substituents. These compounds are sought-after intermediates in organic synthesis, because they allow access, by dealkoxylation according to known methods, to aldehydes and ketones 55 corresponding ethylenic aliphatics. Such a process lends itself particularly well to the synthesis of polyene aldehydes or ketones and in particular of compounds of the terpene series.

T. Mukaiyama et al., “Chemistry Letters”, 1974, pp. 15 to 16; 60 ibid., 1975, pp. 319 to 322, have shown that the condensation of acetals of aldehydes or ketones of variable structure with enoxysilanes derived from aldehydes or enolizable ketones of indifferent nature, in the presence of titanium tetrachloride, leads to the formation of aldehydes or of etheroxide ketones. "In particular, by condensation of a dienoxysilane derived from an α-ethylenic or β, γ-ethylthene enolisable with an acetal derived from an α-ethylenic aldehyde such as acetal and

- 0

(II)

in which :

Ri, R2, R3, R7, Rs, R9 and Rio represent a hydrogen atom or a hydrocarbon radical containing from 1 to 30 carbon atoms, optionally substituted by one or more functional groups inert under the reaction conditions, Rö represents a linear or branched alkyl radical having from 1 to 8 carbon atoms,

R4 and Rs, identical or different, represent hydrocarbon radicals having from 1 to 30 carbon atoms, optionally substituted by one or more functional groups inert in

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4

the reaction conditions, up to one of the symbols R4 and R5 possibly representing a hydrogen atom,

R4 and R5 can also form together with the carbon atom to which they are linked an aliphatic saturated or unsaturated, substituted or unsubstituted ring,

by reaction of an acetal of general formula:

Rr

\

/

GOLD,

(III)

, / \

GOLD,

in which R4, Rs and Rg have the meaning given above, with an enoxysilane of general formulas:

(R) (iv) a

or

R9? 7

l10 "

0- -Si-

R (

8

Jh-n

(V)

■ (R)

n in which:

Ri, R2, R3, R7, Ra, R9 and Rio have the meaning given above, n is equal to 2 or 3,

R represents a hydrocarbon radical having from 1 to 20 carbon atoms.

In the formulas (I) to (V), the various symbols represent more particularly:

R, linear or branched alkyl radicals such as methyl, ethyl, propyl, isobutyl, octyl, pentadecyl radicals; cycloalkyl radicals having 5 to 6 carbon atoms such as cyclopentyl or cyclohexyl radicals; aryl radicals such as the phenyl and naphthyl radicals, optionally substituted by 1 or 2 lower alkyl groups (for example toluyl and xylyl radicals); phenylalkyl radicals containing from 1 to 4 carbon atoms in the alkyl part such as the benzyl and p-phenylethyl radicals; preferably, R represents lower alkyl radicals, cyclohexyl, phenyl and benzyl radicals; the different radicals R carried by the silicon atom can be identical or different.

Ri, R2, R3, R7, Rs, Rö and Rio, identical or different, represent linear or branched alkyl radicals, preferably having from 1 to 25 carbon atoms, optionally substituted by a cycloalkyl or cycloalkenyl radical having from 5 to 6 cyclic carbon atoms; arylalkyl radicals having from 1 to 10 carbon atoms in the alkyl part; cycloalkyl radicals having from 5 to 6 cyclic carbon atoms optionally substituted by 1 to 3 lower alkyl radicals; linear or branched alkenyl radicals preferably having from 2 to 25 carbon atoms and possibly comprising one or more ethylenic double bonds, conjugated or not, optionally substituted by a cycloalkyl or cycloalkenyl radical having from 5 to 6 cyclic carbon atoms; arylalkenyl radicals having 2 to 10 carbon atoms in the alkenyl residue; cycloalkenyl radicals comprising from 5 to 6 cyclic carbon atoms, optionally substituted by 1 to 3 lower alkyl radicals, with however the restriction that, when R2, R3 and R7 5 represent alkenyl or cycloalkenyl radicals, they do not contain a double bond ethylenic conjugated with the enolic double bond; the radicals Ri, R2, R3 and R7 at Rio can be, where appropriate, substituted by functional groups inert with respect to the acetals used in the process, and in particular by nitro, alkoxy groups lower, alkyloxycarbonyl (such as acetoxy, propylcarbonyl-oxy), nitrile, hydroxyl.

R4 and R5 represent linear or branched alkyl radicals preferably having from 1 to 25 carbon atoms, optionally substituted by 1 or 2 cycloalkyl or cycloalkenyl radicals having from 5 to 6 cyclic carbon atoms, optionally substituted by 1 to 3 lower alkyl radicals; cycloalkyl radicals having 5 to 6 cyclic carbon atoms, optionally substituted with 1 to 3 lower alkyl radicals; phenylalkyl radioisols containing from 1 to 4 carbon atoms in the alkyl part; linear or branched alkenyl radicals preferably having from 2 to 25 carbon atoms and which may comprise one or more ethylenic double bonds, conjugated or not, optionally substituted by 1 or 2 cycloalkyl or cycloalkenyl radicals having from 5 to 6 cyclic carbon atoms which may if necessary, carry from 1 to 3 lower alkyl radicals; cycloalkenyl radicals having 5 to 6 cyclic carbon atoms, optionally substituted by 1 to 3 lower alkyl radicals; phenylalkenyl radicals having from 2 to 10 carbon atoms in the aliphatic part; aryl radicals comprising 1 or 2 benzene rings, condensed or not, optionally substituted by 1 to 3 lower alkyl radicals; the radicals R4 and Rs can also be substituted by functional groups such as those mentioned above.

35 Rö represents alkyl radicals having from 1 to 5 linear or branched carbon atoms, such as methyl radicals,

ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-pentyl.

More particularly still, the various symbols appearing in formulas (I) to (V) can take the following meanings given by way of nonlimiting examples:

Ri, R2, R3, R7, Rs, R9 and Rio can be, with the restriction already mentioned for R2, R3 and R7, methyl radicals,

ethyl, propyl, isopropyl, n-butyl, t-butyl, pentyles, decyls, pentadecyls, 2-cyclohexyl ethyl, [1-cyclohexene] -2 "ethyl; arylalkyl radicals such as benzyl, phenyl-2 ethyl; cycloalkyl radicals such as cyclopentyl, cyclohexyl, 2-methyl cyclohexyl, 2,6-trimethyl cyclohexyl; alkenyl radicals such as the vinyl, allyl, 2-methyl allyl, 2-butene-2 yl, 2-methyl-butene-2 yl, 4-methyl-pentene-3 yl, so hexene-3 yl, hexadiene-3,5 yl radicals, 2,4-dimethyl-pentene-3 yl, 3,4-dimethyl-pentene-3 yl, 2,4-dimethyl-2,4-pentadiene, 2,4-dimethyl-2,4,6,8 yl nonatetraene, [trimethyl -2 ', 6', 6 'cyclohexene-1' yle -] - 4, 3-methyl-butene-2 yl; arylalkenyl radicals such as 3-phenyl-2-propene-yl; cyclo-55 alkenyl radicals such as cyclohexene-1 yl, cyclohexene-2 yl, trimethyl-2,6,6 cyclohexene-1 yl.

R "and R5 can be alkyl radicals such as those already mentioned for Ri in Rio; cyclohexylmethyl, cyclo-hexyl-2 ethyl, [cyclohexene-1 'yl] methyl, [trimethyl-2', 6 ', 6' 60 cyclohexene-1 'yl] methyl, [trimethyl-2', 6 ', 6 'cyclohexene-1' yl] -2 ethyl; arylalkyl radicals such as benzyl, 2-phenylethyl; cycloalkyl radicals such as cyclopentyl, cyclohexyl, 4-methoxy cyclohexyl; alkenyl radicals such as vinyl; allyl; methallyl; propene-2 yl-2; propene-1 yl-1; 2,6-methyl-2-propene-yl-1; 1-ethyl-pentene-1 yl-1; dimethyl-2,6 hepta-diene-1,5 yl-1; dimethyl-2,6 heptadiene-1,6 yl-1; trimethyl-2,6,10 undecatriene-1,5,9 yl-1; 2,6-dimethyl heptene-5 yl-1; 2,6-dimethyl heptene-6 yl-1; dimethyl-4,8 nonatriene-1,3,7 yl-1;

5

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hexadiene-1,5 yl-1; 1-methyl-1,5-hexadiene-1-yl; 2-methyl hexadiene-1,5 yl-1; 2,5-dimethyl hexadiene-1,5 yl-1; dimethyl-6,10 undecatriene-1,5,9 yl-1; trimethyl-2,4,6 heptadiene-1,5 yl-1; trimethyl-1,5,9 undecatriene-1,4,8 yl-1; dimethyl-3,8 undeca-tetraene-1,3,7,9 yl-1; 2,6,10, trimethyl 4-ethoxy-undecatriene-1,5,9 yl-1; tetramethyl-2,6,10,14 diethoxy-4,8 pentadecatetra-ene-1,5,10,14 yl-1; [cyclohexene-1 'yl] -2 vinyl; [trimethyl-2 ', 6', 6 'cyclohexene-2' yl] -2 vinyl; [trimethyl-2 ', 6', 6 'cyclohexa-diene-1', 3 'yl] -2 vinyl; [trimethyl-2 ', 6', 6 'hydroxy-4' cyclohexene-1 'yl] -2 vinyl; [trimethyl-2 ', 6', 6 'methoxy-4' cyclohexene-1 'yl] -2 vinyl; [2-trimethyl, 6 ', 6' cyclohexene-1 'yl] -3 methyl-1 propene-1 yl; [trimethyl-2 ', 6', 6 'cyclohexene-1' yl] -3 methyl-1 propene-2 yl; [acetoxy-4 'trimethyl-2', 6 ', 6' cyclo-hexene-1 'yl] -3 methyl-1 propene-1 yl; [2-trimethyl, 6 ', 6' cyclo-hexene-1 'yl] -4 2-methyl-butadiene-1,3 yl; [4-methoxy-2'-trimethyl, 6 ', 6' cyclohexene-1 'yl] -4 2-methyl-butadiene-1,3 yl; [trimethyl-2 ', 6', 6 'cyclohexene-1' yl] -5 methyl-3 pentadiene-1,3 yl; [trimethyl-2 ', 6', 6 'cyclohexene-1' yl] -6 methyl-4 hexatriene-1,3,5 yl; [trimethyl-2 ', 6', 6 'cyclohexene-1' yle] -8 dimethyl-2,6 octatetraene-1,3,5,7 yl, [trimethyl-2 ', 6', 6 'cyclohexene-1' yle] -4 2-methyl-4-ethoxy-2-butene yl; 2,6-dimethyl-4,8-diethoxy [tri-methyl-2 ', 6', 6 'cyclohexene-1' yl] -8 octadiene-1.5 yl; 1,5-dimethyl-4-ethoxy [trimethyl-2 ', 6', 6 'cyclohexene-1' yl] -7 heptadiene-1.5 yl; arylalkenyl radicals such as the 2-phenyl vinyl radical; aryl radicals such as phenyl, o-toluyl, p-methoxy-phenyl.

In the formulas (I) to (V), the various symbols used preferably have the following meaning:

n is equal to 3,

Ri, R2, R3, R7, Rs, R9 and Rio represent hydrogen atoms or lower alkyl radicals and more preferably still methyl and ethyl groups,

R4 and R5 represent:

a) alkyl radicals having from 1 to 10 carbon atoms optionally substituted by a cyclohexyl, cyclohexe-nyl or cyclohexadienyl radical which may contain from 1 to 3 methyl groups,

b) cyclohexyl radicals optionally substituted with 1 to 3 methyl groups,

c) alkenyl radicals having from 2 to 25 carbon atoms such as those already mentioned, optionally substituted by a cyclohexyl or cyclohexenyl or cyclohexadienyl radical comprising, where appropriate, from 1 to 3 methyl groups,

d) cyclohexenyl or cyclohexadienyl radicals, optionally substituted with 1 to 3 methyl groups,

e) benzyl or P-phenylethyl radicals,

f) phenyl radicals.

Even more preferably, one of the radicals R "and R5 symbolizes a hydrogen atom or a methyl group and the other has any of the meanings a), b), c), d), e) and f ). When the radicals R 1 to Rio contain functional groups, the latter are more particularly methoxy, ethoxy, methylcarbonyloxy groups, and their number varies from 1 to 5.

Rö represents a methyl or ethyl group.

The enoxysilanes of formulas (IV) or (V) which are used to carry out the process of the invention are generally known products which are easily prepared, for example by reaction of a mono-, di- or trihalosilane of general formula :

(R) n - Si - (X) 4— n in which R and n have the meaning already given and X represents a chlorine or bromine atom, with an enolizable aldehyde or ketone, i.e. a aldehyde or a ketone comprising at least one hydrogen atom in position a and / or a 'with respect to the carbonyl group. The dienoxysilanes of formula (V) are obtained in the same way from aldehydes or ketones enolizable a, ß- or p, y-ethylenic. The reaction of the halosilanes with the enolizable aldehydes or ketones can be carried out in the presence of zinc chloride and a hydracid acceptor according to the process described in Belgian patent No. 670769.

Among the enoxysilanes of formulas (IV) and (V), non-limiting examples that may be mentioned:

A) Enoxysilanes derived from enolizable aldehydes such as:

vinyloxytrimethylsilane trimethylsilyloxy-1 propene trimethylsilyloxy-1 butene triethylsilyloxy-1 methyl-2 propene methyldiethylsilyloxy-1 pentene triphenylsilyloxy-1 pentadiene-1,4

trimethylsilyloxy-1 methyl-4 pentadiene-1,4

trimethylsilyloxy-1 2,4-dimethyl-1,4-pentadiene

trimethylsilyloxy-1 heptene-1

trimethylsilyloxy-1 ethyl-2 hexene le (butadiene-1,3 yloxy) trimethylsilane le (butadiene-1,3 yloxy) triethylsilane le (butadiene-1,3 yloxy) dimethylethylsilane le (butadiene-1,3 yloxy) triphenylsilane bis - (butadiene-1,3 yloxy) trimethylsilane le (butadiene-1,3 yloxy) dimethylphenylsilane le (methyl-3 butadiene-1,3 yloxy) trimethylsilane l (3-ethyl-butadiene-1,3 yloxy) trimethylsilane -2 butadiene-1,3 yloxy) trimethylsilane (2-ethyl butadiene-1,3 yloxy) trimethylsilane l (hexadiene-1,3 yloxy) trimethylsilane bis- (3-methyl-butadiene-1,3 yloxy) trimethylsilane (4-methyl-pentadiene-1,3 yloxy) trimethylsilane (3-methyl pentadiene-1,3 yloxy) trimethylsilane le (2-methyl-hexadiene-1,3 yloxy) trimethylsilane (3,4-dimethyl-pentadiene-1, 3 yloxy) triethylsilane le (4-cyclohexyl-butadiene-1,3 yloxy) triethylsilane le (dimethyl-3,7 octatriene-1,3,6 yloxy) triethylsilane le (trimethyl-3,7,11 dodecatetraene-1,3,6 , 10 yloxy) trimethylsilane le [(trimethyl-2 ', 6', 6 'cyclohexene-1' yl) -4 methyl l-3 hexadiene-1,3

yloxy] trimethylsilane.

Among these compounds, vinyloxytrimethylsilane, trimethylsilyloxy-1 propene-1, trimethylsilyl-oxy-1 methyl-2 propene-1, trimethylsilyloxy-1 butene-1, trimethylsilyloxy-1 butadiene-1, are preferably used. trimethylsilyloxy-1 methyl-2 butadiene-1,3, trimethylsilyloxy-1 methyl-3 butadiene-1,3, trimethylsilyloxy-1 ethyl-2 butadiene-1,3, trimethylsilyoxy-1 ethyl-3 butadiene-1, 3.

B) Enoxysilanes derived from insoluble ketones such as:

trimethylsilyloxy-2 propene triethylsilyloxy-2 butene-1

2-methyldiethylsilyloxy-2-butene

n-propyldimethylsilyloxy-2-methyl-3-butene-1

2-trimethylsilyloxy-1,3-butadiene

2-phenyldimethylsilyloxy-1,3-butadiene

3-methyl-trimethylsilyloxy-2, butadiene-1,3

trimethylsilyloxy-2 pentene-1

trimethylsilyloxy-2 pentene-2

trimethylsilyloxy-3 pentene-2

trimethylsilyloxy-3 methyl-2 pentene-2

trimethylsilyloxy-2 methyl-4 pentene-2

2-trimethylsilyloxy-1,4-pentadiene

trimethylsilyloxy-3-pentadiene-1,3

trimethylsilyloxy-2-methyl-4,4-hexadiene

2-trimethylsilyloxy-3,4-dimethyl-1,4-hexadiene

trimethylsilyloxy-2 heptene-2

trimethylsilyloxy-3 heptene-2

trimethylsilyloxy-3 heptene-3

trimethylsilyloxy-2 heptene-1

5

10

15

20

25

30

35

40

45

50

55

60

65

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6

trimethylsilyloxy-2 methyl-4 heptene-1 trimethylsilyloxy-2 methyl-4 heptene-2 trimethylsilyloxy-2 methyl-5 heptadiene-1,5 trimethylsilyloxy-2 methyl-5 heptadiene-2,5 trimethylsilyloxy-2 hexadiene- 2,5 trimethylsilyloxy-1,4-hexadiene-1,4 trimethylsilyloxy-2-hexadiene-1,5 trimethylsilyloxy-4 dimethyl-2,6 heptene-3 bis- (propene-2 yloxy) trimethylsilane trimethylsilyloxy-4 pentadiene-1 , 3 methyl-2 trimethylsilyloxy-1,3-pentadiene-1,3 methyl-trimethylsilyloxy-1,3-pentadiene-1,3 methyl-2 trimethylsilyloxy-1,3-hexadiene

As examples of acetals suitable for carrying out the process according to the invention, non-limiting mention may be made of the dimethyl and diethyl acetals of the following aldehydes and ketones:

acetaldehyde propanai n-butanal 2-methyl propanai 3-methyl butanal acrolein 2-methyl acrolein crotonaldehyde tiglic aldehyde senecialdehyde 2-ethyl hexene-2 al geranial the general farnesal citronellal 3,7 dimene octene-7 al citrilydene acetaldehyde heptadiene-2,6 al 2-methyl heptadiene-2,6 al 3-methyl heptadiene-2,6 al dimethyl-7,11 dodecatriene- 2,6,10 al a-sinensal 4,9-dimethyl-dodecatetraene-2,4,8,10 al cyclohexanal cyclohexylacetaldehyde ß-cyclocitral a-cyclocitral safranal 4-isopropyl cyclohexene-1 al [trimethyl-2 ', 6', 6 'cyclohexene-1' yljacetaldehyde methyl-2 [trimethyl-2 ', 6', 6 'cyclohexene-1' yl] -4 butene-2 al methyl-2 [ trimethyl-2 ', 6', 6 'cyclohexene-1' yl] -4 butene-3 al-methyl-2 [trimethyl-2 ', 6', 6 'cyclohexadiene-1', 3 'yl] -4 butene- 2 al methyl-2 [acetoxy-4 'trimethyl-2', 6 ', 6' cyclohexene-1 'yl] -4 butene-2 al methyl-2 [methoxy-4' trimethyl-2 ', 6', 6 'cyclohexene-1 yl] -4 butene-2 al p -ionilydenene acetaldehyde 4-methyl [2-trimethyl, 6 ', 6' -4-methoxy-1 'cyclohexene-1' yl] -6 2,4-hexadiene retinal trimethyl-3,7,11 5-ethoxy-dodecadiene- 2,6,10 al-tetramethyl-3,7,11,15 diethoxy-5,9 hexadecatetraene-2,6,10,14

al 3-methyl-5-ethoxy [2-trimethyl-6 ', 6' cyclohexene-1 'yl] -5 pentene-3 al-3,7-dimethyl-5,9 diethoxy [2-trimethyl-6' , 6 'cyclohexene-1' yl] -9 nonadiene-2,6 al 2,6-dimethyl-5-ethoxy-2 [trimethyl-2 ', 6', 6 'cyclohexene-1' yl] -8 octadiene-2,6 al cinnamaldehyde acetone methyl ethyl ketone methylallyl ketone s mesityl oxide 6-methyl-heptene-5 one-2 pseudo-ionone dehydro-3 ', 4' ß-ionone methoxy-4 'ß-ionone io a-ionone ß-ionone.

The process according to the invention lends itself in particular to the preparation of alkoxy-substituted carbonyl compounds of general formula:

(VI)

20

Jm

In which R 1 to R 6 have the meanings already indicated and m represents an integer ranging from 1 to 10, or carbonyl compounds of general formula:

in which Ri in Rio have the meanings already given and m 'is an integer ranging from 1 to 4.

40 In formulas (VI) and (VII), the various grounds for general formulas:

and

(VIII)

can be the same or different.

To prepare the carbonyl compounds of formulas (VI) and 55 (VII), starting derivatives are those derived from carbonyl compounds of formula (VI) or (VII), in which the number of units of formula (VIII) or ( IX) is equal to (m - 1) or (m '- 1) and which results from a previous operation. It would be possible, without departing from the scope of the present invention, to prepare carbonyl-containing compounds comprising both units of formula (VIII) and of formula (IX). The method according to the invention therefore constitutes a convenient means for increasing from 1 to m and / or 1 to m 'units (VIII) and / or (IX) the skeleton of an aldehyde or of a ketone starting from their acetal , proceeding by successive „condensations.

65

Without the scope of the invention being limited, the condensation of acetals with enoxysilanes can be represented by the following reaction scheme:

7

617,167

(4-n)

-If (R)

not

R ,. GOLD

1 * jx \ £ n 1

* 7 iL O + (RgO) -Si- (R)

\ / 6 U-n n

V

"Ti-n

R2 R3

Rk 0R £

(U-n) +

r / N) R6

The alkoxysilane formed during the reaction is a by-product of industrial interest; it can indeed be used in the synthesis of polysiloxane polymers. It can also be transformed into organohalosilanes by the usual methods, which can again be used for the preparation of the starting enoxysilanes.

The quantities of enoxysilanes and acetals used to conduct the reaction may be close to stoichiometry, that is to say close to 1 mole of acetal per enoxy group present in the enoxysilane, or may be widely spread by using either an excess of one or the other of the reagents. Thus, one could use an amount of acetal of 5 moles per enoxy group involved in the reaction but, in general, it does not exceed 2 moles of acetal per enoxy group. The operation is preferably carried out with an excess of enoxysilane relative to the acetal, this excess having no critical upper limit, the enoxy compound possibly even serving as a solvent when it is liquid under the reaction conditions. When it is not desired to use enoxysilane as solvent, the quantity used can be such that the number of moles of acetal per enoxy group is at least 0.1. Ultimately, the respective amounts of acetal and of enoxysilane can be such that the number of moles of acetal / number of enoxy groups is between 5 and 0.1 and, preferably,

between 2 and 0.1.

The condensation of the acetal with the enoxysilane can be carried out indifferently within an organic solvent inert with respect to the reagents used, or in the absence of any solvent. In the first case, it is possible to use aliphatic (hexane, heptane), cycloaliphatic (cyclohexane), aromatic (benzene) hydrocarbons; ethers (ethyl oxide; tetrahydrofuran; diglyme); halogenated derivatives (chloroform, carbon tetrachloride); nitriles (acetonitrile, propionitrile, benzonitrile); to tertiary carboxamides (dimethylformamide, dimethyl-acetamide, n-methylpyrrolidone).

The temperature at which the reaction is carried out depends on the reagents used. Generally, a temperature between -80 and + 200 ° C and preferably between -20 and 100 ° C is very suitable; the use of the catalysts according to the invention does not however require the use of temperatures below 0 ° C. It is possible to operate at normal pressure or at pressure lower or higher than atmospheric pressure, for example under the autogenous pressure of the reactants under the chosen temperature conditions. A simple test allows in each case to choose the appropriate temperature.

The quantity of catalyst expressed in number of moles of zinc halide or of BF3 or of its complexes can vary within wide limits. In general, 1 × 10 -4 mole to 0.5 mole of catalyst is used per enoxy group present in the enoxysilane and preferably 1 × 10 -3 to 0.2 mole per enoxy group.

As zinc halide, ZnCb and ZnBrç are preferably used; BF3 complexes with ethyl ether, methyl ether, methyl and ethyl ether, isopropyl ether, butyl ether, isoamyl ether, tetrahydrofuran agree well.

The reaction time depends on the conditions chosen, in particular the temperature, and can vary between a few minutes and several hours.

Among the alkoxyaldehydes and ketones corresponding to formulas (I) and (II), there may be mentioned:

2-methyl-3-ethoxy-butanal 3-methyl-3-methoxy-butanal 3-ethoxy-3 hexene-4 al 3-methyl-5-ethoxy-2-hexene al 5-methyl 3-methoxy-4 hexene methyl -6 ethoxy-4 heptene-5 one 2 dimethyl-3,7 ethoxy-5 octadiene-2,6 al 15 dimethyl-3,7 methoxy-3 octene-6 al phenyl-5 ethoxy-3 pentene-4 al 3-methyl-5-phenyl-5-ethoxy-2-pentene 3-methyl-5-ethoxy [2-trimethyl-6 ', 6', 6 'cyclohexene-1' yl] -5-pentene-2 al

20 dimethyl-6,10 ethoxy-4 undecadiene-5,9 one-2

[trimethyl-2 ', 6', 6 'cyclohexene-1' yl] -4 ethoxy-4 butanone-2 trimethyl-3,7,11 ethoxy-5 dodecatriene-2,6,10 al trimethyl-3, 7.11 3-methoxy-dodecadiene-6.10 a [trimethyl-2 ', 6', 6 'cyclohexene-1' yl] -5 3-methyl-3-ethoxy-pentene-4 a [trimethyl-2 ', 6 ', 6' cyclohexene-2 'yl] -5 3-methyl-5-ethoxy-2-pentene al to methyl-4 [trimethyl-2', 6 ', 6' cyclohexene-1 'yl] -6 3-ethoxy -4 to 30 7-phenyl-5-ethoxy-2,6-heptadiene a-4,9-dimethyl-3,10 diethoxy-4,6,8 dial-2,6-dimethyl-5-ethoxy-2 '(trimethyl-2') , 6 ', 6' cyclohexene-1 'yl] -8 octadiene-2,6 al dimethyl-3,7 [trimethyl-2', 6 ', 6 cyclohexene-1' yl] -9 ethoxy-5 35 nonatriene- 2,6,8 al-dimethyl-3,7 diethoxy-5,9 [trimethyl-2 ', 6', 6 'cyclohexene-1' yl] -9 nonadiene-2,6 al dimethyl-3,7 'diethoxy- 5.9 phenyl-9 nonadiene-2,6 al trimethyl-2,7,11 ethoxy-5 [trimethyl-2 ', 6', 6 'cyclohexene-1' 40 yl] -13 tridecapentaene-2,6,8 , 10.12 al.

As already indicated, the alkoxycarbonylated compounds obtained by the process according to the invention are valuable intermediates for obtaining aldehydes and ethylenic ketones such as, in particular, senecialdehyde, citral, farnesal, pseudo -ionone, tiglic aldehyde, ß-ionone, p-ionylidene-acetaldehyde or retinal.

The process described above can be carried out continuously or discontinuously. The following examples illustrate the invention and show how it can be practiced.

Example 1:

Charged under an argon atmosphere:

- citric diethyl acetal 11.3 g (5 • 10 ~~ 2 mole)

- acetonitrile 20 cm3

- zinc chloride 0.125 g (9.2 • 10 _ 4 mole)

the mixture is stirred at room temperature and a solution 60 of 7.8 g (5-10 -2 mole) of trimethylsiloxy-1 methyl-3-butadiene-1.3 is poured into 5 cm 3 of acetonitrile in 5 minutes. Then heated to reflux (78 ° C) and the trimethylethoxysilane is removed by distillation with part of the acetonitrile. The distilled acetonitrile is replaced by an amount sufficient to keep the level of the reactor constant. 65 After 1 h 10 min, it is observed that no trimethylethoxysilane is formed any more (identified on a test sample by gas / liquid chromatography). 58.5% of the theoretically formed trimethylethoxysilane was recovered by distillation.

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The reaction mass is cooled, then 25 cm 3 of ethyl oxide is added thereto and it is neutralized with 25 cm 3 of an aqueous solution at 5% by weight of sodium bicarbonate. Then washed with water, then the organic phase is dried over potassium carbonate. The ether is removed by distillation under 20 mm of mercury. 11.2 g of a fraction distilling between 100 and 130 ° C. are recovered under 0.45 mm of mercury, in which we identify and dose by infrared spectrometry, nuclear magnetic resonance and by vapor phase chromatography, 9.5 g of trimethyl-3,7,11 ethoxy-5 dodecatriene-2,6,10 al. The yield is 72.5% relative to the loaded acetal.

The ethoxyaldehyde Cis thus obtained was deethoxylated as follows:

1.8 g of ethoxyaldehyde C15 are charged under argon in a three-tube 100 cm3 flask, stirred by a magnetic bar and equipped with a coolant, an argon inlet, a Vigreux column with coolant. (6.8 • 10 ~ 3 mole), 50 cm3 of anhydrous toluene, 5 mg of hydroquinone and 6 mg of p-toluenesulfonic acid (3.16 -10—5 mole).

Stir and heat to reflux. The toluene is slowly distilled and replaced over time, so as to keep a constant level in the reactor. Toluene causes ethanol formed by azeotropy.

After 1 h 35 min of heating, the mixture is cooled, 10 cm 3 of ether are added and neutralized with 25 cm 3 of a 5% solution of sodium bicarbonate. Wash with water and dry over sodium sulfate. The solvents are removed under 20 mm of mercury and distilled. A fraction of 1.15 g is obtained, distilling at 120-140 ° C under 0.2 mm of mercury.

The NMR examination shows that we are in the presence of 67% of C15 aldehyde (including 48% of the all trans form). There remains 13% of starting C15 ethoxyaldehyde.

Example 2:

In a three-necked flask of 50 cm3 equipped with a stirrer, a condenser and a dropping funnel, the following are charged under an argon atmosphere:

- diethyl citral acetal 4.5 g (2 • 10 ~~ 2 mole)

- acetonitrile 10 cm3

- zinc chloride 0.05 g (3.68 • 10 ~ 4 mole)

the mixture is stirred at ambient temperature and a solution of 2.6 g (2 -10-2 mole) of 2-trimethylsilyloxy in 5 cm 3 of acetonitrile is poured in 5 minutes. The temperature rises from 24 to 27 ° C in 1 hour. Then heated to reflux (78 ° C) for VA h. Cooled, washed with 30 cm3 of a 5% solution of sodium bicarbonate, taken up in 30 cm3 of ether and washed with 30 cm3 of water. Dried over sodium sulfate, filtered, concentrated ether and acetonitrile,

then distilled under vacuum; the following fractions are obtained:

Fi Eb 2.5 min 75-105 0.3 g F2 105-119 3.8 g grading 87%

in dimethyl-6,10, ethoxy-4 undecadiene-5.9 one-2 (chromatographic assay), which represents a yield of 69%.

The deethoxylation of this product at the reflux of toluene in the presence of paratoluenesulfonic acid leads to pseudo-ionone with a yield of 86%, ie an overall yield of 59% relative to the citral acetal.

Example 3:

The procedure is as in Example 1 with the following amounts of reactants:

- citral diethyl acetal 4.52 g

- acetonitrile 10 cm3

- zinc chloride 0.1 g

- trimethylsilyloxyisoprene 3.12 g

After 2V * h at reflux, the reaction mass is treated as in Example 1.

3.8 g of C15 ethoxyaldehyde are dosed (a yield of 73.5% relative to the loaded acetal).

Example 4:

The procedure is as in Example 3, but loading 0.05 g of ZnCk and replacing the acetonitrile with 10 cm3 of hexane. Maintained 50 minutes at reflux. By distillation, 3.45 g of a fraction passing between 115 and 120 ° C under 0.15 mm of mercury and which contains 95% of C15 ethoxyaldehyde are collected. The yield relative to the loaded acetal is 62%.

Example 5:

The procedure is as in Example 4, but replacing the hexane with ethyl acetate. First heated 45 min at 50 ° C, then 30 min at reflux. 3.34 g of Ci5 ethoxyaldehyde are then assayed in the distillate of the reaction mass. The yield is 64% compared to the loaded acetal.

Example 6:

In the apparatus described in Example 1, 4.52 g of diethyl citral acetal (2-10-2 mole) and 3.12 g of trimethyl-siloxyisoprene (2-10 "2 mole) are charged. establishes a stream of argon and stirred at room temperature, a solution in 5 cm3 of anhydrous ether of 0.05 cm3 of boron trifluoride etherate titrating 45% by weight of BF3 (3.68%) is added over 5 min. 10 ~ 4 mole) Agitation is carried out for 1 hour at ambient temperature, then the mixture is heated to 50 ° C. while removing the ether. After 45 minutes at 50 ° C., the mixture is heated for 1 hour at 60 ° C. The mixture is cooled and 20 cm 3 are added. Ether is neutralized with 25 cm 3 of a 5% solution of sodium bicarbonate, washed with water and dried over potassium carbonate, the ether is eliminated under 20 mm of mercury and a fraction of 2.9 g passing between 85 and 130 ° C under 0.3 mm of mercury and titrating 53% in ethoxyaldehyde C15 by gas / liquid chromatography.

Example 7:

In the apparatus described in Example 1, 7.25 g of diethyl acetal of β-cyclocitral (3.2-10 -2 mole), 20 cm 3 of dry acetonitrile and 60 mg are charged under a stream of argon. zinc chloride (4.4-10 ~ 4 mole). Stirred at room temperature and added in 5 min 6.25 g of trimethylsiloxyisoprene (4-10 ~ 2 mole) in 5 cm3 of dry acetonitrile.

It is heated for 1 hour at reflux, then cooled. 20 ml of ether are added and neutralized with 25 ml of a 5% solution of sodium bicarbonate. Wash with distilled water and dry over potassium carbonate. The ether is removed under 20 mm of mercury. A fraction of 8 g is distilled passing between 90 and 120 ° C under 0.4 mm of mercury. NMR analysis and the IR spectrum confirm the structure of the expected C15 cyclic ethoxyaldehyde. Yield on loaded acetal: 94.5%. The product obtained has the following refractive index: nD20 1.5053.

The cyclic ethoxyaldehyde Ci 5 was deethoxylated in the apparatus used in Example 1 and operating as follows:

1.8 g of Ci 5 ethoxyaldehyde (6.8 • 10 -3 mole), 50 cm 3 of anhydrous toluene, 2 mg of hydroquinone and 6 mg of p-toluenesulfonic acid (3.16-10) are loaded under argon. -5 mole).

Stir and heat to reflux. The toluene is slowly distilled and replaced over time so as to keep a constant level in the reactor. After A h of heating, 3 mg of p-toluenesulfonic acid (1.58 × 10 -5 mol) are again introduced and the reaction is continued.

The disappearance of the ethoxyaldehyde is monitored by thin layer chromatography. The test is stopped after 3 h of heating. Cool and add 10 cm3 of ether. Neutralized with 25 cm3 of an aqueous solution at 5% by weight of sodium bicarbonate. Wash with water and dry over sodium sulfate. The solvents are removed under 20 mm of mercury and distilled. A fraction of 1.1 g is obtained passing between 100-140 ° C under 0.3 mm of mercury.

The NMR examination shows that we are in the presence of 44% of C15 aldehyde (including 26% of the all trans form). There remains 23% of starting C15 ethoxyaldehyde.

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Example 8:

In the apparatus described in Example 1, 3.38 g of diethyl acetal of C5 ethoxyaldehyde prepared in Example 1 (1 ■ 10 -2 mole) are charged under an argon stream, 10 cm 3 of acetonitrile. dry and 25 mg of zinc chloride (1.84-10 ~ 4 mole). The mixture is stirred at room temperature and 1.56 g of trimethyl-silyloxyisoprene (1 × 10 -2 mole) dissolved in 5 cm 3 of dry acetonitrile are added over 5 min.

It is maintained for 45 minutes at room temperature, then heated for 1 hour at reflux. Cool, add 20 cm3 of ether and neutralize with 20 cm3 of a saturated sodium bicarbonate solution.

Wash with distilled water and dry over potassium carbonate. The ether is eliminated under 20 mm of mercury, then under 0.5 mm of mercury. 4 g of a slightly oily yellow liquid are obtained, titrating 95% of C20 diethoxyaldehyde by NMR.

■ Yield on loaded acetal: 95%.

The acetal of ethoxyaldehyde C15 was obtained by the action of ethyl orthoformate in ethanol in the presence of p-toluenesulfonic acid. It is a product of refractive index nD20 1.4684 and of Ebo, 5 = 135 ° C.

Example 9:

In the apparatus described in Example 1, 5.9 g of diethyl acetal of C15 cyclic ethoxyaldehyde obtained in Example 7 (1.74-10 -2 mole) are charged under a stream of argon. cm3 of dry acetonitrile and 45 mg of zinc chloride (3.3 • 10 -4 mole). The mixture is stirred at room temperature and 2.8 g of trimethylsilyloxyisoprene dissolved in 5 cm 3 of dry acetonitrile are added over 5 min.

It is heated for 1 hour at reflux. Cool and add 20 cm3 of ether. Neutralized with 25 cm3 of an aqueous solution at 5% by weight of sodium bicarbonate. Wash with water and dry over potassium carbonate. The ether is first removed under 20 mm of mercury, then under 0.5 mm of mercury, 7.1 g of a slightly syrupy yellow liquid is obtained, the titer established by NMR is 95% diethoxyretinene. The IR spectrum is in agreement with the expected structure.

Yield on loaded acetal: 95%.

Example 10:

In the apparatus described in Example 1, 4.77 g of diethyl acetal of 2 [trimethyl-2 ', 6', 6 'cyclohexene-1' yl] -4 methyl-2 are charged under a stream of argon butene-2 al (C14 aldehyde)

(1.7 • IO-2 mole), 10 cm3 of dry acetonitrile and 45 mg of zinc chloride (3.3 • IO-4 mole).

Stirred at room temperature and added in 5 min 2.81 g of trimethylsiloxy-1 methyl-2-butadiene-1,3 (1.8 -10-2 mol) dissolved in 5 cm3 of dry acetonitrile.

It is heated for 1 hour at reflux. Cool and add 20 cm3 of ether. Neutralized with 25 cm3 of an aqueous solution at 5% by weight of sodium bicarbonate. Wash with water and dry over potassium carbonate. The ether is removed under reduced pressure (0.5 mm of mercury). 5.3 g of a slightly viscous product are obtained, the IR spectrum and NMR of which confirm the expected structure of the C19 cyclic ethoxyaldehyde.

Yield on loaded acetal: 93%.

Example 11:

17.7 g (1.5 ■ 10 "1 mole) are loaded into a 250 cm3 three-necked flask equipped with a stirrer, a condenser, a dropping funnel and an argon inlet. diethyl acetal of acetaldehyde dissolved in 40 cm3 of dry acetonitrile and 3 g of zinc chloride (2.2-10-2 mole).

Under a stream of argon, 39 g of trimethylsiloxy-1 propene-1 (3 × 10 −1 mole) are poured in solution in 25 cm 3 of acetonitrile. The mixture is heated to reflux and the A h is maintained at 78 ° C. It is cooled and neutralized with 150 cm 3 of a 5% solution of sodium bicarbonate. After extraction with ether, drying over sodium sulphate and evaporation of the solvent, 14.7 g of a distilling fraction are obtained by distillation at 88-90 ° C under 100 mm of mercury.

By vapor phase chromatography, 97% of 2-methyl-3-ethoxy-butanal is determined, the structure of which is confirmed by nuclear magnetic resonance.

The yield is 75.5%.

The deethoxylation of this product in formic acid at reflux led to tiglic aldehyde with a yield of 44% in pure isolated product.

Example 12:

In the apparatus described in Example 1, 6.97 g of diethyl acetal of α-cyclocitral (3.1 • 10 -2 mole), 15 cm 3 of dry acetonitrile are charged under a stream of argon. 96.3 mg of zinc chloride (7.1 ■ IO-4 mole).

Stirred at room temperature and poured in 7 min 6.13 g of trimethylsiloxyisoprene (3.93-10 ~ 2 mole) in 3.5 cm3 of dry acetonitrile.

It is heated for 3 h 20 at reflux, then cooled. 20 ml of ether are added and neutralized with 25 ml of a 5% solution of sodium bicarbonate. Wash with distilled water and dry over potassium carbonate. The ether is removed under 20 mm of mercury. In addition to the unreacted starting material, a 4.7 g fraction passing between 100 and 130 ° C. is distilled under 0.5 mm of mercury. CGL analysis gives a yield on a product transformed by 44% into 3-methyl-5-ethoxy [2-trimethyl, 6 ′, 6 ′ cyclohexene-2 ′ yl] -5 pentene-2 al.

Example 13:

In a three-necked 50 cm3 flask equipped with mechanical stirring, a condenser, a dropping funnel, 4.76 g of diethyl citral acetal (2-10-2 mole) are charged under a stream of argon. ) and 50 mg of zinc chloride (3.68-10 -4 mole). Stirred at room temperature and poured 3.12 g of trimethyl-sililoxyisoprene (2-10 "2 mole) in 3 min. The temperature rises from 22 to 35 ° C in 5 min, then goes down again.

The mixture is heated and distilled under vacuum in a device equipped with a trap cooled by an acetone / dry ice mixture. A fraction of 1.25 g is collected passing at 85 ° C under 760 mm of mercury.

0.8 g of a liquid product is also recovered from the trap. The fraction titers 96% in trimethylethoxysilane and the trap 45.5%. Recovery yield of trimethylethoxysilane: 66.3%.

The reaction mass is diluted with 15 cm3 of ether and neutralized with 10 cm3 of a saturated solution of sodium bicarbonate. After washing and drying over sodium sulphate, the ether is eliminated under 20 mm of mercury and a fraction of 4.15 g is distilled passing between 100 and 120 ° C. under 0.5 mm of mercury and titrating 90% in ethoxyaldehyde C15 by Vapor chromatography.

Yield on loaded acetal: 70.7%.

Example 14:

In a three-necked flask of 50 cm3, equipped with mechanical stirring, a coolant, a dropping funnel, the following are charged under an argon atmosphere:

- prenatal diethyl acetal 31.6 g (2-10 "1 mole)

- acetonitrile 50 cm3

- zinc chloride 0.373 g (2.748 • 10 ~ 3 mole) The mixture is stirred at ambient temperature and a solution of 32.76 g (2.1 ■ 10_I mole) of 1-trimethylsiloxy-3-methyl-butadiene-1 is poured in 5 minutes, 3 in 20 cm3 of acetonitrile. The temperature rises from 23 to 28 ° C during casting. Then heated to reflux (78 ° C) for 45 min. The reaction mass is cooled and the acetonitrile is concentrated under a pressure of 20 mm of mercury.

The reaction mass is neutralized with 50 cm3 of a saturated sodium bicarbonate solution. 20 cm3 of ethyl oxide are added. The organic phase is decanted and washed with 2 x 20 cm3

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distilled water. Dried over sodium sulfate. The ether is removed under 20 mm of mercury and distilled. 32.4 g of dimethyl-3.7 5-ethoxy-octadiene-2.6 al are obtained, dosed by gas / liquid chromatography and by NMR, in 2 fractions, the main one of which distills at 82 ° C. under 0.3 mm of mercury.

Yield on loaded acetal: 82.6%.

Example 15:

9.5 g of dimethyl acetal (tri-methyl-2) are charged under an argon atmosphere in a 50 cm3 three-necked flask equipped with mechanical stirring, a condenser, a dropping funnel ', 6', 6 ', cyclohexene-1' yl) -5 methyl-3 pentadiene 2.4 al (C15 aldehyde) (3.6-10 ~ 2 mole) 25 cm3 of dry acetonitrile and 92.75 mg of zinc chlorate (6.82-10 ~ 4 mole). Stirred at room temperature and poured in 5 min 5.694 g of trimethylsiloxy-1 methyl-3-butadiene-1,3 (3.65-10 "2 mole) dissolved in 10 cm3 of dry acetonitrile.

The mixture is heated at reflux (78 ° C.) for 1 h. Cooled and added 50 cm3 of ethyl oxide. The reaction mass is neutralized with 25 cm 3 of a saturated sodium bicarbonate solution. Wash with distilled water and dry over sodium sulfate. The ether is removed under 20 mm of mercury. A fraction of 10.02 g passing between 160 and 170 ° C is distilled under 0.01 mm Hg.

NMR analysis and the IR spectrum confirming the structure of the expected methoxyretinene.

Yield on loaded acetal: 88.3%.

The demethoxylation of methoxyretinene was carried out as follows:

1.5 g of methoxyretinene (4.74-10 "3 mole) are loaded into argon in a 50 cm3 three-necked flask, equipped with mechanical agitation, a condenser, a dropping funnel , 10 cm3 of dichloromethane and 10 cm3 of acetonitrile, the mixture is stirred at ambient temperature and a rapid flow of 2.87 g of 1.5-diaza-bicyclo (5,4,0) undecene-5 (DBU) dissolved in 4 cm3 of dichloromethane 10 and 4 cm 3 of acetonitrile 1 g of 4 A molecular sieve is added, in 2 mm diameter beads.

The mixture is heated to reflux (60 ° C.). The disappearance of methoxyretinene is followed by thin layer chromatography. The test is stopped after 2 h of heating. The reaction mass is cooled and neutralized with 1.24 g of acetic acid in solution in 10 cm 3 of distilled water. 10 cm3 of ethyl oxide are added. Wash with water and dry over sodium sulfate. The ether is eliminated under 20 mm of mercury, then under 0.5 mm. 1.5 g of a dark red viscous product are obtained. Analysis by pressure liquid chromatography gives a yield of 55% of retinene in the following ratio of isomers:

- 13 eis 21.7%

- 9 eis 13.1%

25 - t. trans 65.2%.

15

Claims (12)

617,167 1. Process for the preparation of ketones and aliphatic aldehydes comprising an alkoxy group in position β or 8 relative to the carbonyl group, by reaction of an acetal of an aliphatic aldehyde or ketone with an enoxysilane derived from a aliphatic aldehyde or an aliphatic ketone, in the presence of a catalyst, characterized in that the latter is chosen from the group formed by zinc halides, boron trifluoride and its complexes. 2. Method according to claim 1, characterized in that aldehydes and ketones of general formulas are prepared: (D and ai) in which: Ri, R2, R3, R7, R8, R9 and Rio represent a hydrogen atom or a hydrocarbon radical having from 1 to 30 carbon atoms, optionally substituted by one or more inert functional groups, R6 represents a linear or branched alkyl radical having from 1 to 8 carbon atoms, R4 and R5, identical or different, represent hydrocarbon radicals having from 1 to 30 carbon atoms, optionally substituted by one or more inert functional groups, one at most of the radicals R4 and R5 being able to represent a hydrogen atom, R4 and R5 can also form, together with the carbon atom to which they are linked, an aliphatic ring, saturated or not, substituted or not, by reaction of an acetal of general formula: E5 \ / 0B6 V * ^ oe6 with an enoxysilane of general formulas: (III) R R. 2v R 3i (R) n (IV) jk-n or _0 (V) • If (R) not 2 3 617,167 - cyclohexyl radicals optionally carrying 1 to 3 methyl groups, - alkenyl radicals having from 2 to 25 carbon atoms, optionally substituted by 1 cyclohexyl, cyclohexenyl, cyclohexadienyl radical which can bear from 1 to 3 methyl groups, s - cyclohexenyl or cyclohexadienyl radicals optionally comprising from 1 to 3 methyl groups, - benzyl radicals, p-phenylethyls, - phenyl radicals, Rö represents a methyl or ethyl group. io 3. Process for the preparation of aldehydes and ketones according to claim 2, characterized in that, in formulas (I) to (V): R represents a linear or branched lower alkyl radical, 4. Method according to one of claims 1 to 3, characterized in that, in formulas (I) to (V): n is equal to 3, mi R represents lower alkyl, cyclohexyl, benzyl and phenyl radicals, - Ri at R3 and R7 at Rio represent hydrogen atoms, lower alkyl radicals, R4 and R5 represent: f'-s - alkyl radicals having from 1 to 10 carbon atoms optionally substituted by a cyclohexyl or cyclohexenyl or cyclohexadienyl radical which can bear 1 to 3 methyl groups, 4-n in which: Ri, R2, R3, R4, R5, Rô, R7, Rs, R9 and Rio have the meaning already given, n is 2 or 3, 5. Method according to one of claims 2 to 4, characterized in that the radicals Ri to R7 and R7 to Rio comprise one or more nitro, lower alkoxy, alkyloxycarbonyl groups, nitrile, hydroxyl. 5? lower alkyls, R6 represents an alkyl radical having from 1 to 5 carbon atoms. 5 "lower, - phenylalkenyl radicals having from 2 to 10 carbon atoms in the aliphatic part, - aryl radicals comprising 1 or 2 benzene rings, condensed or not, optionally substituted by 1 to 3 radicals 5 R represents a hydrocarbon radical having from 1 to 20 carbon atoms. 6. Method according to one of claims 1 to 5, characterized in that chloride chloride is used as the zinc halide. 7. Method according to one of claims 1 to 6, characterized in that the amount of catalyst expressed in moles per enoxy group present in the enoxysilane is between 1 x 10-4 and 0.5. 20 8. Method according to one of claims 1 to 7, characterized in that the amount of acetal expressed in moles per enoxy group is between 5 and 0.1. 9. Method according to one of claims 1 to 8, characterized in that the reaction is carried out at a temperature between 25 - 80 and 200 ° C, at equal, higher or lower pressure than atmospheric pressure. 10. Method according to one of claims 1 to 9, characterized in that the reaction is carried out in an inert solvent. 10 cyclohexyl, benzyl, phenyl, Ri to R3, R7 to Rio represent: - linear or branched alkyl radicals having from 1 to 25 carbon atoms, optionally substituted by a cycloalkyl or cycloalkenyl radical having from 5 to 6 carbon atoms 15 cyclicals, - arylalkyl radicals having from 1 to 10 carbon atoms in the alkyl part, - cycloalkyl radicals having from 5 to 6 cyclic carbon atoms, optionally substituted by 1 to 3 alkyl radicals 20 lower, - linear or branched alkenyl radicals having 2 to 25 carbon atoms, which may comprise one or more ethylenic double bonds, conjugated or not, optionally substituted by a cycloalkyl or cycloalkenyl radical having 25 5 to 6 cyclic carbon atoms, - arylalkenyl radicals having from 2 to 10 carbon atoms in the alkenyl part, - cycloalkenyl radicals having from 5 to 6 cyclic carbon atoms optionally substituted by 1 to 3 alkyl radicals 30 lower, R2, R3 and R7 not comprising, when they are alkenyl or cycloalkenyl radicals, an ethylenic double bond conjugated with the enolic double bond, R4 and R5 represent: 35 - linear or branched alkyl groups such as those defined for Ri, - cycloalkyl or cycloalkenyl radicals having from 5 to 6 cyclic carbon atoms, optionally substituted by 1 to 3 lower alkyl radicals, 40 - phenylalkyl radicals containing from 1 to 4 carbon atoms in the alkyl part, - alkenyl radicals, linear or branched having from 2 to 25 carbon atoms and which may contain one or more ethylenic double bonds, conjugated or not, optionally 45 substituted by a cycloalkyl or cycloalkenyl residue having 5 to 6 carbon atoms and being able to carry from 1 to 3 lower alkyl residues, - cycloalkenyl radicals having from 5 to 6 cyclic carbon atoms, optionally substituted by 1 to 3 alkyl radicals 11. Method according to one of claims 1 to 10, characterized in that the acetals used are diethyl acetals of acetaldehyde, citral, ß-cyclocitral, α-cyclocitral, [trimethyl -2 ', 6', 6 'cyclohexene-1' yl] -4 methyl-2 butene-2 al, trimethyl-3,7,11 5-ethoxy-dodecatriene-2,6,10 al, methyl-3 ethoxy -5 [trimethyl-2 ', 6', 6 'cyclohexene-1' yl] -5 pentene-2 al. 35 12. Method according to one of claims 1 to 11, characterized in that one uses as enoxysilane trimethylsilyloxy-1 propene, trimethylsiloxy-2 propene, trimethylsilyloxy-1 methyl-3-butadiene-1,3 and trimethylsilyloxy -1 methyl-2-butadiene-1,3. 40 dimethyl of crotonaldehyde or cinnamic aldehyde, it is possible to obtain a, P-ethylenic aldehydes comprising an alkyloxy residue in position 8; thus, by reaction of the dimethyl acetal of crotonaldehyde with trimethylsilyl-oxy-4-butadiene-1,3, one obtains the 5-methoxy-octadiene-2,6 al-1 which, by demethoxylation, can give access to octatriene -2.4.6 al. Despite its advantage, this type of reaction cannot find industrial application due to the fact that it involves the implementation of particularly low reaction temperatures, of the order of -40 to -78 ° C., and particularly large amount of titanium tetrachloride, since substantially equimolecular amounts of reactants and catalyst are used. Furthermore, in the case where the acetal used does not derive from an ethylenic aldehyde, the course of the reaction requires the joint use of TÌCI4 and an alkyl titanate such as isopropyl titanate.